Sealed antenna



Oct. 12, 1948. B. TREVOR 2,451,

SEALED ANTENNA Filed Dec. 1, 1943 INVENTOR Bertram/ Wavar ATTORNEY- Patented Oct. 12, 1948 SEALED ANTENNA Bertram Trevor, Riverhcad, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application December 1, 1943, Serial No. 512,441

2 Claims.

1 The present invention relates to ultra-high frequency antennas, and particularly to such antennas which are so constructed as to be sealed against the effects of moisture and weather conditions.

An object of the present invention is to decrease the efi'ect of Weather and moisture on the operation of ultra-high frequency antennas.

Another object of the present invention is the provision of a weatherproof ultra-high frequency antenna.

Still another object of the present invention is the provision of a weatherproof ultra-high frequency antenna which may be readily adjusted and easily mounted on a coaxial line.

The foregoing objects and others which may appear from the following detailed description are attained by the provision of a half wave doublet radiator and a pair of quarter wave chokes all enclosed within a sealed low loss plastic case for weather protection. The case is so sealed that the entire antenna system may be maintained under a few pounds pressure of dry nitrogen gas.

Referring now to the single figure of the drawlng showing in longitudinal cross section an embodiment of the present invention, TL denotes a coaxial transmission line having an outer shell I and an inner conductor 2. The transmission line is adapted to be connected between the antenna and suitable transducer equipment which is not shown. The outer and inner conductors of the transmission line are cut off flush at one end. The outer shell has a coupling flange soldered or otherwise hermetically attached to the end. The inner conductor 2 has an extending rod 3 soldered to its end. Rod 3 is maintained in coaxial alignment with the central aperture through coupling flange 5 by an insulating washer or button 6 inserted in the aperture of the coupling flange 5.

An outer tubular sleeve member 1 is associated with and surrounds rod 3. It carries at one end a coupling flange 9 adapted to be clamped to coupling flange 5 by means of bolts 10 and II. The flange may be soldered or brazed as desired to tubular member I. The apertures in flange 9 through which bolts II! and l I pass are preferably threaded so that flange 9 may be clamped to flange 5 without requiring the use of any clamp ing nuts. A hermetically sealed junction between flanges 5 and 9 is assured by the interposition of a gasket l2.

A pair of quarter wave chokes I l and 16 are arranged to be adjustably positioned along the 2 length of tube 1. Each of the quarter wave chokes includes an outer sleeve member 18 threadedly mounted on a bushing I9. The effec tive electrical length of each of the chokes may be adjusted to one quarter of the'operating wave length by running sleeve l8 a suitable distance onto' bushing l9.

Set screws 20 and 2| are provided for locking each of the quarter wave chokes It and IS in place. Once the quarter wave chokes have been located on the tube 1, an insulating button 22 is slipped over the extending end of rod 3 and clamped into position by a lock nut 24. The insulating button 22 has a shoulder on one side which engages with the inner bore of tube-1 to maintain the coaxial alignment of rod 3 within tube 1.

An adjustable end portion 25 of the doublet radiator is finally screwed onto the threaded end of rod 3 and is so adjusted that the overall length extending out of tube 1 is approximately one quarter of the desired operating wave length. Choke I4 is secured on tube 1 in such position that the distance from the open end of the choke to the bottom of the extending quarter wave portion of the doublet is also approximatel a quarter Wave length. Thus, the extending portion of the doublet acts as the top half of a vertical half wave radiator, while the quarter wave portion of tube 1 extending beyond the quarter wave choke M acts as the other half of the doublet.

The distance between the open ends of chokes M and I6 is preferably adjusted to approximately a half wave length whereby they aid. one another to prevent the flow of high frequency energy along the outside of the line. Once the antenna has been adjusted to the proper dimensions for the frequency at which it is to operate, a cover including a base flange 2'! a tubular sleeve 28 and an end closure 29 is slipped over the antenna and clamped into position by nuts 30 and 3| engaging bolts I0 and H. Lock washers 32, 32 are provided to prevent nuts 39 and 3! from loosening. Also, a suitable gasket 33 should be interposed between flanges 21 and 9 to assure a hermetic seal between the cover and the remainder of the system.

In order to prevent the condensation of moisture within a transmission line, it is common practice to keep the line under a few pounds pressure of dry nitrogen gas. The present antenna is so designed that it may be operated in the same manner. Before the plastic cover is bolted into place, a dry nitrogen tank may be connected through an appropriate fitting (not shown) to 3 the coaxial line and nitrogen allowed to flow through the line until the air within the line and antenna has been replaced.

Small apertures 36 are provided in each of the insulating spacers 6 and 22 to permit the flow of gas through the system. As soon as it has been determined that dry nitrogen is issuing from the antenna end of the system, the plastic cover is bolted into place and the desired pressure built up in the line. Since the antenna system is as hermetically sealed as the remainder of the line, the desired pressure will be maintained with substantially no loss.

While I have illustrated a particular embodiment of the present invention, it should be clearly understood that it is not limited thereto since many modifications may be made in the several elements employed and in their arrangement, and it is therefore contemplated by the appended claims to cover any such modifications as fall within the spirit and scope of the invention.

Having now described my invention, what I claim as new and desire to have protected by Letters Patent is: 1 i

1. An antenna system including a section of coaxial line including an outer shell and in inner conductor, said inner conductor extending from one end of said outer shell a distance equal to approximately one quarter of the operating wave length, the other end of said outer shell bearing a coupling flange for hermetic connection to a further coaxial transmission line, a tubular insulating casing closed at one end and carrying a coupling flange at the other end, and coaxially arranged with respect to said outer shell, said outer shell and inner conductor being maintained in coaxial relationship by insulating spacing washers, said spacing washers having perforations therein to permit the flow of a fluid from said further coaxial line between said outer shell and said inner conductor and between said outer shell and said casing, and means for clamping the coupling flange of said casing in a fluid-tight relationship to the coupling flange of said outer shell.

. 2. An antenna system as set forth in claim 1 in which a pair of quarter wave traps are so arranged along said outer shell within said insulating casing as to prevent the flow of radio frequency energy along the outside of said shell. BER'IRAM TREVOR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,557,049 Hammond, Jr Oct. 13, 1925 1,797,534 Wyrick Mar. 10, 1931 1,981,058 Marconi et al Nov. 20, 1934 2,149,415 Berndt Mar. 7, 1939 2,229,733 Goldman Jan. 28, 1941 2,237,792 Roosenstein Apr. 8, 1941 2,267,951 Roosenstein Dec. 30, 1941 2,274,389 Von Baeyer et al. Feb. 24, 1942 2,322,971 Roosenstein June 29, 1943 2,332,952 Tischer et al Oct. 26, 1943 2,413,187 McCurdy Dec. 24, 1946 2,421,593 Bishop June 3, 1947 

